The fabs which are build to be 450mm-ready are quite known such as Intel and TSMC. Samsung is also "hot" as Dylan says. Then there are some R&D/pilot ready facilities such as IMEC and CNSE has plans (they have already a couple of 450mm tools).
Intel is the main force pushing for 450, yes, but TSMC and Samsung are also hot for it. I'd guess the other big foundries and some of the memory companies may also adopt it, but I don't think they'll be first in line.
This forecast assumes a lot, like how do they know that how many of the fabs which are going to be constructed are of 450mm and what is cost implication of going from 300 to 450mm, I believe it should reduce if taken per wafer or per sqcm. The 450 mm fabs are not actually demanded by the supply side but more of a move toward higher sizes to reduce cost per die. And who are they guessing are going for 450mm- Intel, yes but who else?